This invention relates to a hydrogen purification process, and especially to a process wherein hydrogen is produced from hydrocarbons by partial oxidation, the resulting gaseous fraction is fed to a CO conversion unit, and the acid gases are removed by scrubbing.
The production of hydrogen by partial oxidation of, e.g., fuel gases, fuel oils, residues or coal comprises the process steps of: (a) synthesis gas formation alternatively termed gasification; and (b) CO shift conversion. In the gasification step, a gas consisting essentially of H.sub.2, CO, CO.sub.2, H.sub.2 0 and inert gases is obtained. The equilibrium conditions for the CO shift conversion generally are reached at a high temperature, e.g. 1400.degree. C. in the gasification reactor. When heavy oil is used, H.sub.2 and CO are contained in the gas in about equal parts. To maintain the resultant equilibrium conditions, the crude gas is cooled rapidly by direct and/or indirect quenching. To raise the H.sub.2 yield, the resultant gas is passed to the shift converter where it is saturated with steam and the CO therein is catalytically converted to CO.sub.2 and H.sub.2. Then the gas is cooled, the excess steam condensed out and the gas fed to the H.sub.2 S removal and then to the CO.sub.2 removal, which preferably is performed by absorption with an organic, physical solvent. (A physical solvent is a solvent which does not enter into a chemical reaction with any components of the system). For additional details of the production of hydrogen by partial oxidation, reference is invited to the literature, e.g, Faith, Keyes and Clark's "Industrial Chemicals", Fourth Edition, Lowenheim and Moran, John Wiley & Sons, N.Y. 1975, pages 470, 471, 469, incorporated by reference herein.
By the process, a product with a purity of 97 to 98.5% hydrogen is obtained. With subsequent methanation, the CO and CO.sub.2 content can be reduced to values less than 10 ppm, but at the expense of a lowered yield of H.sub.2 which is consumed in the catalytic methanation reaction. Instead of methanation, a pressure swing adsorption installation can be used, with which a hydrogen purity of up to 99.99% by volume is achieved, but with about 10% of the amount of product lost. The pressure swing adsorption installation reaches its limits of economical use in the case of high product pressures about 40 bar which, however, are desirable in various cases, i.e. NH.sub.3 -synthesis, hydrogenation and desulfurization.